Purpose We aimed to measure 1) the dynamics of locomotor fatigue during constant supra-critical power cycling and 2) the magnitude of any reserve in locomotor power at intolerance to constant and ramp-incremental cycling in recreationally active volunteers. Methods Fifteen participants (7 women and 8 men, 22 ± 3 yr, 3.34 ± 0.67 L·min−1 V˙O2peak) completed ramp-incremental and very-heavy constant power (205 ± 46 W) exercise to the limit of tolerance. Immediately after intolerance, the ergometer was switched into the isokinetic mode, and participants completed a short (~5 s) maximal isokinetic effort at 70 rpm. The time course of locomotor fatigue during constant supra-critical power exercise was characterized with these short maximal isokinetic sprints at 30, 60, 120, and 180 s and at the limit of tolerance. Each bout was terminated after the isokinetic sprint. Results Constant power exercise duration was 312 ± 37 s. Isokinetic power production values at 30, 60, 120, and 180 s and at the limit of tolerance (at 312 ± 37 s) was 609 ± 165, 503 ± 195, 443 ± 157, 449 ± 133, and 337 ± 94 W, respectively. Of the total decline in isokinetic power, ~36% occurred within the first minute of exercise, and significant (P < 0.05) reductions in isokinetic power occurred at all time points versus the baseline maximal isokinetic power (666 ± 158 W). In addition, a significant power reserve of 132 ± 74 W (64% of the task requirement) and 119 ± 80 W (47%) was present at the limit of constant power and ramp-incremental exercise, respectively. Conclusions Locomotor fatigue occurred rapidly during supracritical power exercise with pseudo-exponential kinetics. Instantaneous isokinetic power production at the limit of tolerance exceeded that of the task requirement, regardless of the constant or ramp work rate profile. Thus, the perceptual and physiologic limits were dissociated at the limit of tolerance in recreationally active volunteers.

Introduction Amassing evidence suggests that post-awakening salivary cortisol rhythms (changes in cortisol throughout the day) may indicate health status. We previously established summary parameters for salivary cortisol in U.S. Navy Sea, Air, and Land and reported excellent parameter stability across 2 days of repeated sampling. To confirm the generalizability of our original findings to other military populations, we replicated the procedures of our prior report in another specialized military group. The purpose of this study was to (1) establish summary parameters of daily salivary cortisol rhythms, (2) evaluate summary parameter stability, and (3) assess the impact of sampling compliance in U.S. Navy Explosive Ordnance Disposal (EOD) technicians. Materials and Methods Seventy active duty, male Explosive Ordnance Disposal technicians (mean ± SD age; 34.9 ± 6.5 years) self-collected saliva samples in a nondeployed setting on two consecutive weekdays at WAKE, WAKE + 30 min, WAKE + 60 min, 4 p.m., and 9 p.m. For salivary cortisol, we computed summary parameters, i.e., measures of magnitude and measures of pattern, and then evaluated their stabilities via correlational analyses and Cronbach’s alpha (α). Compliance was objectively and subjectively evaluated using actigraphy and self-reported data, respectively. This research was conducted under a Naval Health Research Center Institutional Review Board approved study (NHRC.2015.0013). Results Average salivary cortisol concentrations increased at WAKE + 30 (mean ± SE reactivity; 48.9 + 6.8%) from WAKE, followed by a swift recovery at WAKE + 60. Approximately 10.9% of the group were classified as negative-responders (i.e., &lt; 0% change from WAKE to WAKE + 30). The measures of magnitude demonstrated fair stability across two days (r value range: 0.37-0.45, ps &lt; 0.01; α range: 0.54-0.62). Fifty-five percent of the sample was classified as compliant (defined as &lt;15 min deviation from target sampling times) across both days. Compliance decreased to 31% when compliance criteria were refined to &lt;5 min deviation; however, controlling for compliance did not overwhelmingly influence the more stable summary parameters of magnitude. Conclusions These findings demonstrate a thorough replication, with some additional refinement, of our prior study, implying generalizability across diverse military populations. Study limitations include unsupervised saliva collection in a free-living setting, which is counterbalanced by ecological validity. The noninvasive salivary sampling protocol used in this study yields stable estimations of daily cortisol rhythms in specialized military men and is recommended as an operational health surveillance tool by which to monitor chronically stressed military members.